1. Field of the Invention
The present invention pertains to the art of electronic display modules, and more particularly, to the attachment of components such as bezels and reflectors relying upon heat staking to surface mount display modules.
2. Art Background
Electronic displays are used in a variety of devices to display information to the user. A variety of technologies are used, including Liquid Crystal Displays (LCD), Vacuum Fluorescent Displays (VFD), and Light Emitting Diode displays (LED).
With the development of brighter and more colorful LED materials, LED displays are becoming more popular.
These displays are typically produced as subassemblies or components for inclusion in more complex devices. A display is typically manufactured on a small printed circuit board which contains the display material, LED, LCD, or VFD. It is often desirable to mount a plastic component such as a bezel or reflector to the display circuit board to shape or improve the display. A bezel serves a number of purposes, from protecting the display elements to directing and diffusing light from elements such as LEDs, adding legends or descriptive information, and the like. The bezel is typically made from a plastic or thermoplastic material, and is attached to the display circuit board by heat staking a plurality of mounting stakes from the bezel through mounting holes on the display circuit board. Similarly, and particularly for LED displays, a reflector may also be used to diffuse and couple light from LED chips mounted to the display circuit board. This reflector is typically mounted to the display circuit board by heat staking.
The process of heat staking involves passing a plastic member called a stake through a mounting hole in the display circuit board. The stake is heated, deforming the plastic material to cover part of the surrounding display circuit board, securing the stake in place.
The completed display circuit board must be connected to the larger electronic assembly. One approach is to provide a connector on the display circuit board, allowing connections to be made to the larger assembly. Another approach is to provide connecting pins or a leadframe base on the display circuit board, providing it with leads similar to those used in integrated circuit packages. Neither of these approaches is desirable, as they add cost and complexity to not only the display module, but also to the overall device.
Many electronic devices manufactured today use surface-mount techniques, where components are mounted and soldered in place on the surface of a circuit board.
It is desirable to treat display modules as surface-mountable components. Doing so allows the use of automated assembly equipment, reducing manufacturing time and cost. To be suitable for surface mount, the bottom surface of the display module must be precisely planar. Irregularities in the bottom surface of the display module introduce soldering problems when mounting the display module to the larger device, such as poor wetting, open connections, solder bridging, and solder joint deformation.
Unfortunately, heat staking produces irregularities in the lumps of thermoplastic formed during the heat staking process. These irregularities must be reworked to make the display circuit board suitable for use in a surface-mount environment. This rework is not only time consuming and therefore costly, but if significant material is removed, the holding strength provided by the stake is weakened considerably.